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Unit 1 Biology
Semester 1: Exam Revision ANSWERS
These questions supplement information but are NOT the only ones you need to know. Thoroughly revise
notes, questions in your textbook, tests, Biozone and Outcome Tasks. Don’t forget interactive crosswords and
podcasts, too.
1. What is the Cell Theory? What tool is used to observe cells? What units are they measured with?
The cell theory is one of the basic principles of biology. The cell theory arose in the mid 1800’s. The cell theory
states….
- All living organisms are composed of cells. They may be unicellular or multicellular.
- The cell is the basic unit of life.
- Cells arise from pre-existing cells.
(The cell theory recognises that all living things are composed of one or more cells and that new cells are
produced by existing cells)
Microscopes are used to give enlarged images of cells and the structures they contain, and make it possible for
us to examine cells with great detail. The unit of measure often used in relation to cell size is the micrometre
(µm). 1000µm= 1mm
2. Distinguish between prokaryotic and eukaryotic cells, AND between cytoplasm and cytosol AND between
anabolism and catabolism.
Prokaryotic cells have relatively undefined internal structures and they also lack a clearly defined
structure to house their DNA. Organisms that are made up of prokaryotic cells are called
prokaryotes and consist of all bacteria and archeans, which are another group of microbes.
Eukaryotic cells have a much more complex structure than prokaryotic cells. All Eukaryotic cells
contain many different kinds of membrane bound structures called organelles suspended in the
cytosol. These organelles include a nucleus with a clearly defined membrane called a nuclear
envelope. The DNA of a eukaryotic cell is located in the nucleus. Organisms made up of
eukaryotic cells are called eukaryotes and include all animals, plants, fungi and protists, the single
celled organisms. The nucleus of a eukaryotic cell is usually visible with a light microscope, but
many organelles in this cell can only be viewed with an electron microscope.
The chloroplast is another organelle that can be easily seen through a light microscope.
Cytosol is the fluid that is inside each living eukaryotic cell that consists primarily of water
containing many dissolved substances. (it is not found in prokaryotic cells)
The Cytoplasm is the material surrounding the nucleus of a cell. It consists of a matrix in which
the cell’s organelles are suspended. The cytoplasm may be differentiated into the dense outer
ectoplasm, which is primarily concerned with cell movement and the less dense endoplasm,
which consists of most of the cell’s structures.
3. What is meant by the term partially or differentially permeable in relation to the cell plasma membrane?
Partially (differentially) permeable describes a boundary that allows only some materials to pass through it.
Plasma membranes of cells are partially permeable as they allow only some dissolved materials to cross it.
Due to the presence of a partially permeable membrane surrounding cells, they are able to maintain the
internal environment by controlling the movement of substances in and out the cell.
4. Which of the following is an energy-requiring process? - Osmosis, diffusion, active transport, facilitated
diffusion
Make sure you know about each of these processes
DIFFUSION (No Energy Required)
-
The movement of molecules from an area of high concentration to low concentration. Diffusion stops
when both sides are equal or isotonic.(note that by saying that diffusion stops it means that the net
movement of molecules into the cell becomes equal to the net movement of molecules out of a cell)
The example below shows diffusion of sugar molecules in water moving from an area of high concentration to
low concentration. the high concentration of sugar molecules, over time moves across the semipermeable
membrane until the solution on each side is isotonic.
SEMIPERMEABLE MEMBRANE – is a membrane that is selective or only lets some dissolved substances through. It
is only partially able to be passed through.
OSMOSIS (No Energy Required)
-
A specific ‘type of diffusion’, it is the movement of only WATER across a semipermeable membrane.
The movement of water from a hypertonic solution(higher in concentration) across a semipermeable
membrane to a hypotonic solution(lower in concentration) until both sides become isotonic (equal in
concentration)
The net movement of water across a partially permeable membrane without an input of energy and
down a concentration gradient. The movement of water from an area of high concentration of water (low
concentration of solutes or hypotonic) to an area of low concentration of water (high concentration of
solutes or hypertonic)
FACILITATED DIFFUSION (No Energy Required)
-
Type of diffusion where the movement of molecules is assisted by carrier proteins. The molecules are
still moving from an area of high to low concentration (down a concentration gradient) therefore no
energy is needed. Facilitated diffusion is used to move substances that can’t diffuse across the
phospholipid bilayer of plasma membranes.
ACTIVE TRANSPORT (Energy Required)
-
Movement of molecules in or out of a cell against a concentration gradient of from a low
concentration(hypotonic) to a high concentration (hypertonic).
This is not passive movement and requires energy in the form of ATP (adenosine triphosphate) the movement
of low to high does not occur naturally therefore it need to physically be moved.
Active transport is the way that plants (usually) get their water + minerals from the soil.
5. Define these terms as they relate to materials crossing a cell membrane: gradient, equilibrium, hypertonic,
hypotonic, endocytosis, exocytosis, phagocytosis, pinocytosis
gradient- The rate of change in growth, metabolism, or physiological activity of a cell or organism.
equilibrium- The condition in which all acting influences are balanced or cancelled by equal opposing
forces, resulting in a stable system.
Hypertonic- Having a greater degree of tone or tension. Having a higher osmotic pressure in a fluid
relative to another fluid. Pertaining to a solution (e.g. extracelllular fluid) with higher solute
concentration compared with another. A solution that has a higher concentration of dissolved
substances than the substance to which it is compared.
hypotonic- having a lesser degree of tone or tension, as in a ‘hypotonic muscle’. having a lesser osmotic
pressure in a fluid compared to another fluid. refers to a solution with a comparatively lower concentration
of solutes compared to another. A solution that has a higher concentration of dissolved substances than
the substance to which it is compared.
endocytosis- A process in which cell takes in materials from the outside by engulfing and fusing them
with its plasma membrane.
exoctosis- The process in which the cell releases materials to the outside by discharging them as
membrane-bounded vesicles passing through the cell membrane.
phagocytosis- The ingestion of bacteria or other material by phagocytes and ameboid protozoans.
A form of endocytosis that involves bulk movement of solid particles into a cell
Pinocytosis- The ingestion of liquid into a cell by the budding of small vesicles from the cell membrane.
A form of endocytosis that involves bulk movement of liquids into a cell
6. What is meant by the Surface Area to Volume (SA:V) ratio? Why is it important for a cell to have a high SA:V?
What happens to the SA:V ratio as a cell increases in size? How do some cells or organisms increase their SA?
SA:V ratio is a measure of the number of units of SA available for every unit of internal area
It is important for cells to have a high SA:V ratio to enable them to survive as a high SA:V ratio
allows sufficient movement of nutrients into cells however a low SA:V means that the rate of
exchange is too slow to allow the cell to receive its required nutrients
The larger the cell, the lower the SA:V ratio due to cells increasing their internal volume faster then
their SA increases when the size of a cell increases.
Having really small cells (or whole organisms) enables a high SA:V ratio.
7. Make up a table to summarise the function of these cell structures: cell nucleus, mitochondria, ribosomes,
endoplasmic reticulum, Golgi apparatus, vesicles, lysosomes, chloroplasts, vacuoles, cilia, flagella.
Organelle
Function
Cell nucleus
Contains DNA, it is the control centre of the cell
Mitochondria
Site of energy production in cellular respiration
ribosome
Synthesis of protein
Endoplasmic reticulum
Transports substances within the cell
Golgi apparatus
Stacks of membranes that package materials in vesicles for
export
Vesicle
Membrane-bound sac
Lysosome
Site of digestion within a cell
Chloroplast
Site of photosynthesis and storage of starch
Vacuole
Structures filled with fluid (materials + pigments in solution) large in plant cells
Cilia
(in eukaryotes) whip-like structures involved in cell movement
Flagella
(in bacteria and eukaryotes) whip-like organelle, involved in
movement
8. From the human body, list examples of different cells / tissues / organs / systems
This is a very broad question and would most likely take several pages to fully complete, but here are a short list of
the basic cells/ tissues/ organs and systems in the human body. They each represent an ascending level of
organisation in the body.
Cells (level of organisation 1): The cell is the basic structural, functional and biological unit of all known
living organisms.
 Red Blood cells (erythrocytes)
 White Blood cells (leucocytes)
 Stem Cells
 Sex Cells (Ova and sperm)
 Nerve Cells
 Specialised cells for each organ (e.g liver or brain cells)
 Skin cells
Tissues (Level of organisation 2): Any of the distinct types of material of which animals or plants are made,
consisting of specialized cells and their products




Connective Tissue
Muscle Tissue
Epithelial Tissue
Nervous Tissue
Organs (Level of organisation 3): A distinct part of an organism that performs one or more specialized functions.

Heart




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Liver
Lungs
Kidneys
Brain
Testicles
Ovaries
Systems (Level of organisation 4): A group of physiologically or anatomically complementary organs or parts





Nervous system
Musculoskeletal system
Renal System (kidneys)
Lymphatic System
Circulatory System
Mixed questions:
a. If you were viewing cells under a microscope, what features could help you determine if they are plant or
animal?
Plant or animal:
Plant cells will have cell walls, while animal cells won’t. SOME Plant cells have chloroplasts (not all cells are
photosynthetic) as well and are more rectangular in shape. plant cells usually have large vacuoles
Prokaryote or eukaryote:
Prokaryotic cells don’t have membrane bound organelles therefore they lack a lot of detail. They also lack a
nucleus (their DNA is dispersed in their cell). Eukaryotic cells are more complex- they have membrane bound
organelles.
b. Is the major site of ATP production the same in a plant cell as in an animal cell? Explain.

In plants- Chloroplasts and mitochondria- Photosynthesis occurs in chloroplasts but cellular
respiration in mitochondria.
 In animals- in mitochondria- Cellular respiration in mitochondria
ATP is produced in the mitochondria in the process of cellular respiration.
(photosynthesis takes place in chloroplasts, the second (light independent) stage of photosynthesis uses
C02 + H+ + ATP = C6H1206 + ADP, so if anything ATP is USED in the chloroplasts
c. A scientist wishes to examine ribosomes. Where should they look – in the nucleus or in the cytoplasm?
Ribosomes are found in the cytosol of cells
d. Identify the following as true or false and briefly justify your answers.
i). Plant cells without chloroplasts can capture the energy of the sunlight.
False.
The chloroplast contains a green pigment called chlorophyll which absorbs the light from the sun.
ii). Chloroplasts can be seen through a light microscope.
True.
Chloroplasts are visible under a light microscope, but to discern their specific detail an electron
microscope must be used.
e. List at least 2 structures that involved in the process of making protein. What is the contribution of each
organelle to this process?







Ribosome - Where the synthesis of protein occurs, amino acids join to form proteins
Nucleus - involved in sending the ribosome (by mRNA) the code for the protein that needs to be made.
Endoplasmic reticulum - involved in transporting the protein, (rough ER)
Nucleolus – rRNA production making protein
Mitochondrion – provides energy for protein synthesis
Endoplasmic reticulum – series of channels for transport of protein, involved in transporting the protein,
(rough ER)
Golgi body – structure that packages protein for transport out of the cell
f. Name the organelle involved in each of these functions:
Control entry and exit of substances: Cell Membrane
internal transport system: The Endoplasmic Reticulum
energy source of the cell: Mitochondria
‘self destruct button’ for cell: Lysosomes (do not actually make the decision)
Organelles containing a large range of digestive enzymes used primarily for digestion and removal of excess
or worn-out organelles, food particles, and engulfed viruses or bacteria.
site of packaging for export from the cell: The Golgi Complex
9. Why is water so vital for living organisms? What are hydrophilic substances? What are hydrophobic
substances?
Water is the most abundant compound in our bodies, it facilitates metabolism,( it is also versatile due to its
cohesive nature).
Hydrophilic (polar)- substances that readily dissolve in water
Hydrophobic (non-polar) - substances that tend to be insoluble in water (but can dissolve in fat/ lipids)


Water is the predominant solvent (a substance in which another substance is dissolved) in all living
organisms
Water molecules are highly cohesive (The intermolecular attraction by which the elements of a body are held
together) because of the attraction between hydrogen and oxygen atoms.
10. How do hydrophobic and hydrophilic parts of phospholipids influence the way they form cell membranes?
As the glycerol end of a phospholipid bilayer is hydrophilic while the fatty acid ends are hydrophobic, the
glycerol ends tend to go on the outside while 2 layers of fatty acids are formed on the inside, this occurs
because cells have fluid outside them (extracellular fluid/ tissue fluid) as well as fluid within them
(intracellular fluid/ cytosol) therefore the side that is attracted to water will form the outside layer while the
hydrophobic fatty acid ends tend to stay in the inside layer.

Hydrophilic: Refers to substances that dissolve easily in water; also called polar (outside and insideblue balls {Glycerol} on diagram below)

Hydrophobic: refers to substances that tend to be insoluble in water; also called non polar (centre
of membrane- Fatty acid tails)
11. What is PHOTOSYNTHESIS? Memorise the balanced equation for photosynthesis. Who does it? Where
does it happen? What in? What is needed for it to happen?
Photosynthesis is a process by which plants tap the radiant energy of sunlight and convert CO2 and H2O
into the organic molecule, glucose and at the same time release oxygen.

BOTH LIGHT ENERGY AND VHLOROPHYLL ARE NEEDED
Plant cells photosynthesise, it happens in photosynthetic cells, it occurs in the chloroplasts of photosynthetic
cells. Sunlight, CO2 and water and chloroplasts with chlorophyll are all needed for photosynthesis to occur.
12. Why is CELLULAR RESPIRATION vital for all living things? What are its reactants? What are the products?
Memorise the balanced equation. What are two difference between aerobic and anaerobic respiration?
Cellular Respiration is vital for all living things as it is the way in which ATP is formed through the release
of energy during cellular respiration of glucose. ATP (Adenosine Triphosphate) is required to maintain
cellular functions and hence is required to maintain life.
Reactants  Products
Glucose + Oxygen  Carbon Dioxide + Water
C6H12O6 + 6O2

6CO2
+ 6H2O
Cell Respiration using Oxygen is termed Aerobic Respiration
Cell Respiration without Oxygen is termed Anaerobic Respiration
Anaerobic Respiration is far less efficient forming only 2 molecules of ATP per 1 Glucose molecule as
opposed to Aerobic Respiration creating 36 ATP molecules per 1 Glucose molecule
In humans, a by-product of Anaerobic Respiration is Lactic acid and Carbon Dioxide
(in humans)
Aerobic respiration
Anaerobic respiration
Oxygen or no oxygen
Present
Absent
Number of ATP molecules released
36- 38 molecules
2 molecules
End products
CO2 + H2O
CO2 + C3H6O3 (lactic acid)
13. ATP is often described as the energy currency of all cells. How does it store energy for cell functions?
Adenosine triphosphate (ATP) – compound that is the common source of chemical energy for cells and
whose structure comprises one adenosine molecule and three phosphate molecules.
The energy required to maintain cellular functions is in the form of ATP.
ATP is required for….
 Manufacturing chemicals
 New tissue and structure production
 Excretory system
 Digestive system
 Nervous tissue
 Muscle contraction
ATP stores energy in its bonds. ATP releases energy when the third phosphate breaks off and Adenosine
triphosphate then becomes adenosine di phosphate (ADP)

NOTE- In exams you must write Adenosine Triphosphate once with ATP in brackets. For the rest of
the exam you can use ATP as long as it was in brackets. This is the same for Adenosine Diphosphate
(ADP)
 Adenosine triphosphate (ATP)- then you can just use ATP
 Adenosine diphosphate (ADP)- then you can just use ADP
l. Define autotrophs and heterotrophs.
An autotroph is an organism that uses the process of photosynthesis or chemosynthesis to create its
own food. This organism can be a plant or Protist. Some of these organisms include The Corpse Lily,
Living Rocks and algae. A heterotroph cannot produce their own food and strive on consuming other
organisms to survive. Most common heterotrophs are humans and animals.
m. List the inputs and outputs of i. Light dependent stage and ii. Light independent stage of Photosynthesis
How does one stage lead into the other?


The first set of reactions depends on the availability of light and the presence of chlorophyll.
The second set of reactions is independent of light but depends on the products of the first set.
Energy (ATP) is required by the second stage, and the first stage producing it by converting ADP to ATP
Hydrogen ions are required by the second stage and the first stage provides it by breaking up a water
molecule into separate oxygen molecules and hydrogen molecules.
The ADP that remains after the second stage is then used by the first stage again to convert it to ATP
n. How do structures in plants increase the efficiency of photosynthesis?
LEAVES…
- Flat shape provides large SA exposed to sunlight
- The many stoma (pores) on one or both leaf surfaces provides access into the leaf for carbon dioxide.
- The thinness and presence of internal air spaces in leaves enables the ready diffusion of carbon dioxide to
photosynthetic cells in the leaf tissue.
- The extensive network of vascular tissue contains xylem tissues to transport water to photosynthetic cells
and phloem tissues to transport the products of photosynthesis from photosynthetic cells to
nonphotosynthetic cells throughout a plant.
STEMS
- Xylem vessels and fibers give rigidity to a stem and assist in its upright stance.
- Branching of stems allows layers of leaves at different levels of a plant, therefore increasing total area
available for sunlight.
ROOTS
- An extensive root system uses a significant volume of soil for water and mineral salts.
- Root hairs have a high SA to V ratio.
THE CHARACTERISTICS OF LEAVES, STEMS AND ROOTS ENSURE THAT THESE STRUCTURES COMBINE TO PROVIDE
ENERGY IN SUNLIGHT, CARBON DIOXIDE AND WATER THAT A PLANT REQUIRED FOR HOTOSYNTHESIS.
o. Why is digestion necessary in heterotrophs?
DIGESTION: Chemical breakdown of large organic molecules into smaller units that can pass across plasma
membranes.
p&q. Define trachea, larynx, lungs, bronchi, bronchioles, alveoli.
Definition
In vertebrates: Tube leading from the larynx to the bronchi (windpipe)
In insects: air filled tubes leading from spiracle openings into the body
Larynx
Chamber containing vocal cords located between the pharynx and the trachea
Lungs
Organ with many alveoli sacs that are present in land vertebrates and function in gas
exchange
Bronchi
Airways in the lungs
Bronchioles Smaller branches of bronchi
Alveoli
Microscopic air sacs, their moist surfaces are the sire of gas exchange in the lung
Trachea
r. Explain how a diffusion gradient is created in the lungs. Describe how gas exchange actually works between
capillaries in the alveoli. Where does newly oxygenated blood go?
The pressure of oxygen on one side gives the gradient that will drive the diffusion in the capillaries that line the
sacs inside the lungs that expand when air is taken in. the alveoli and capillaries in the lungs exchange oxygen for
carbon dioxide.
Where does newly oxygenated blood go? The newly oxygenated blood goes back to the heart. It enters the heart
via the pulmonary vein, goes into the left atrium, left ventricle and then through the aorta where it is taken to the
body.
s. Describe the process of breathing in humans. How does it work?
The process of breathing in and out is known as inspiration and expiration. When we breathe in,
the air enters the nose and moves into the nasal cavity. Coarse hairs filter large particles and the
air becomes moist and is warmed by the blood in the capillaries. The air is then transported from
the nasal cavity into the pharynx/ throat. The air from the pharynx now enters the larynx/voice
box and then it moves into the trachea/windpipe. After that, air is transported into two bronchi
which go into the lungs and branches into smaller and smaller tubes called bronchioles. When air
is taken into these structures, oxygen is absorbed into the body and carbon dioxide which is a
waste product of cells is released. Each bronchiole leads into an alveolar duct which transports
the air into an alveolar sac which is surrounded by small pouches called alveoli. Here air
consisting of carbon dioxide travels from the alveoli in the alveolar sac through the alveolar duct
and up the bronchioles and into the lungs. Then the air travels into the bronchi and returns to the
trachea, then up the larynx and into the pharynx. After that, it exits the body via the nasal cavity,
where the process began.
t. Describe how some non-mammals can achieve efficient gas exchange.
Non-mammals such as plants can achieve efficient gaseous exchange through their specialised
structures. Green plants carry out photosynthesis, a process where light energy is transformed into
chemical energy stored in sugars. For photosynthesis to occur, a plant must have photosynthetic cells
(chloroplasts). These chloroplasts are typically located in the leaves of a plant. Such leaves contain many
pores known as stomata. Each stoma is surrounded by two guard cells. The stoma opens or closes
depending on the turgor of the guard cells. If the guard cells have high water content then they are
turgid and the pore is open. As the guard cells lose water they become flaccid and the pore closes.
Effectively, when the guard cells are high in water and open their stoma to allow water out, they take in
carbon dioxide, a necessary reactant for photosynthesis. This ability of the plant to recognise when it is
able to lose water for the intake of carbon dioxide adds to its efficiency. There are many other ways in
which a plants gas exchange efficiency is increased such as the presence of root hairs with a purpose of
increasing the surface area available for gas exchange
 Fish: Fish utilize counter-current exchange to obtain as much oxygen in the blood as the water
flows in one direction and is the most oxygen-rich at the beginning of the flow, thus the blood
flows opposite to it to reach that said beginning. Insects do not have capillaries for the
movement of oxygen; the oxygen is simply directed through the spiracles, through trachea and
directly into the tissue itself.
u. Why is water loss an inevitable part of excretion in humans? How can this water loss be minimised?
 When protein is metabolised in a cell, ammonia is formed. Ammonia is toxic to cells and must be excreted
Immediately in lots of water or converted into some other nontoxic compound.
 Water is required for to expel nitrogenous waste.
 Can be minimised by the water being reabsorbed at the end.
v. Review Vascular System (XYLEM/PHLOEM) in plants and describe how they allow efficient distribution of
materials. Why is water loss an inevitable part of plant photosynthesis? How can the water loss be
minimised?
Xylem and phloem are the vascular tissue of plants, they can be somewhat compared to human’s arteries and
veins, although the structures of xylem and phloem are very different. The reason xylem are able to transport
water and minerals throughout the whole plant is because water vapour is lost through the stomata, and the
water is sucked or pulled up due to the loss of water through the stomata. The process of moving water through
xylem is called transpiration. The name for moving photosynthetic material (sucrose) in phloem is called
translocation. The process of translocation requires energy and phloem is a more complicated structure than
xylem. Sugar (sucrose) is actively transported from phloem to cells and therefore requires energy, provided by
companion cells.
Water is an inevitable part of photosynthesis because the water is split into hydrogen and oxygen. Also, the
stomata must be open in order for the intake of carbon dioxide to occur, therefore water in the cell can evaporate
out. Often in very dry conditions, plants will try to close the stoma in order to minimise water loss.
Water loss is bound to occur in plant photosynthesis because the process of photosynthesis itself requires water
as an input product, as well as this, the stomata of photosynthetic cells must be open for gas exchange to occur so
that CO2 can be taken in to be used in photosynthesis and excess oxygen to diffuse out into the atmosphere.
Water loss can be minimised by e.g. locating stomata in ‘pits’ other ways include the opening and closing ability of
stomata.
w. How do plants get the gases they need for metabolic processes?
During day, through photosynthesis, they produce O2 taking in CO2 and water ( H2O ).The
chloroplasts absorb photons (smallest part of sunlight) and this photon is used to split water into
H+ and OH- ions 4OH gives 2 H2O and O2 and oxygen is produced. They use some of O2 for
photo-respiration (respiration of the cells which take part in photosynthesis)and rest diffuses out.
They take in O2 during day also, for respiration.
During night,they absorb O2 from the atmosphere through stomata mainly(lenticels and cuticles
also) & give out CO2